A5105883337- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- Astrophysical Phenomena and Observations
- History and Developments in Astronomy
- Calibration and Measurement Techniques
- Solar and Space Plasma Dynamics
- Spectroscopy and Chemometric Analyses
- Spectroscopy and Laser Applications
- Geophysics and Gravity Measurements
- CCD and CMOS Imaging Sensors
- Scientific Research and Discoveries
- Optical Systems and Laser Technology
- High-pressure geophysics and materials
- Semiconductor Lasers and Optical Devices
- Astronomical and nuclear sciences
- Space Exploration and Technology
- Pulsars and Gravitational Waves Research
- Spectroscopy Techniques in Biomedical and Chemical Research
- Advanced Measurement and Metrology Techniques
Indian Institute of Astrophysics
2016-2025
The University of Tokyo
2023
California Institute of Technology
2023
University of Florida
2008-2016
Michigan State University
2005-2011
University of Copenhagen
2011
Universidade de São Paulo
2008-2011
Joint Institute for Nuclear Astrophysics
2005-2010
Osservatorio Astronomico di Padova
2010
Uppsala University
2010
The Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey obtained ≈240,000 moderate-resolution (R ∼ 1800) spectra from 3900 Å to 9000 of fainter Milky Way stars (14.0 < g 20.3) a wide variety spectral types, both main-sequence evolved objects, with the goal studying kinematics populations our Galaxy its halo. are clustered in 212 regions spaced over three quarters sky. Radial velocity accuracies at 18, degrading 20. For signal-to-noise ratio >10 per resolution element,...
Using effective temperature and metallicity derived from SDSS spectra for ~60,000 F G type main sequence stars (0.2
We describe the development and implementation of Sloan Extension for Galactic Exploration Understanding (SEGUE) Stellar Parameter Pipeline (SSPP). The SSPP is derived, using multiple techniques, radial velocities, fundamental stellar atmospheric parameters (effective temperature, surface gravity, metallicity) AFGK-type stars, based on medium-resolution spectroscopy ugriz photometry obtained during course original Digital Sky Survey (SDSS-I) its extension (SDSS-II/SEGUE). also provides...
We present VLT-UVES Li abundances for 28 halo dwarf stars between [Fe/H]=-2.5 and -3.5, 10 of which have [Fe/H]<-3. Four different T_eff scales been used. Direct Infrared Flux Method (IRFM) has used on the basis 2MASS infrared photometry. H_alpha wings fitted against synthetic grids computed by means 1D LTE atmosphere models, assuming self-broadening theories. Finally, a grid profiles 3D hydrodynamical models. The I doublet at 670.8 nm to measure A(Li) NLTE spectral syntheses. An analytical...
In this Letter, we announce the discovery of a new dwarf satellite Milky Way, located in constellation Canes Venatici. It was found as stellar overdensity north Galactic cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The satellite's color-magnitude diagram shows well-defined red giant branch well horizontal branch. As judged from tip branch, it lies at distance ~220 kpc. Based on SDSS data, estimate an absolute magnitude MV ~ -7.9, central surface brightness μ0, V 28 mag...
We validate the accuracy and precision of current SEGUE (Sloan Extension for Galactic Understanding Exploration) Stellar Parameter Pipeline (SSPP), which determines stellar atmospheric parameters (effective temperature, surface gravity, metallicity) radial velocities (RVs), by comparing these estimates selected members three globular clusters (M 13, M 15, 2) two open (NGC 2420 67) to literature values. Spectroscopic photometric data obtained during course original Sloan Digital Sky Survey...
Context.The primordial lithium abundance is a key prediction of models big bang nucleosynthesis, and its in metal-poor dwarfs (the Spite plateau) an important, independent observational constraint on such models.
We report high-resolution spectroscopy of 125 field stars previously observed as part the Sloan Digital Sky Survey and its program for Galactic studies, Extension Understanding Exploration (SEGUE). These spectra are used to measure radial velocities derive atmospheric parameters, which we compare with those reported by SEGUE Stellar Parameter Pipeline (SSPP). The SSPP obtains estimates these quantities based on SDSS ugriz photometry low-resolution (R ∼ 2000) spectroscopy. For F- G-type high...
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r<20 and proper-motion measurements derived from SDSS POSS astrometry, including ~170,000 radial-velocity the spectroscopic survey. Distances to are determined photometric parallax relation, covering distance range ~100 pc 10 kpc over quarter sky at high Galactic latitudes (|b|>20 degrees). find that in region defined by 1 <Z< 5 3 <R< 13 kpc, rotational velocity for disk smoothly decreases, all three...
We estimate the frequency of carbon-enhanced metal-poor (CEMP) stars among very stars, based on an analysis 349 with available high-resolution spectra observed as part Hamburg/ESO R-process Enhanced Star (HERES) survey. obtain that a lower limit 21% ± 2% [Fe/H] ≤ -2.0 exhibit [C/Fe] ≥ +1.0. These fractions are higher than those have been reported by recent examinations this question, substantially smaller samples stars. discuss source difference and suggest in order to take into account...
We present a method for the determination of [alpha/Fe] ratios from low-resolution (R = 2000) SDSS/SEGUE stellar spectra. By means star-by-star comparison with degraded spectra ELODIE spectral library and set moderately high-resolution 15,000) medium-resolution 6000) stars, we demonstrate that are able to measure (with S/N > 20/1) precision better than 0.1 dex, stars atmospheric parameters in range Teff [4500, 7000] K, log g [1.5, 5.0], [Fe/H] [-1.4, +0.3], over [-0.1, +0.6]. For < -1.4, our...
Carollo et al. have recently resolved the stellar population of Milky Way halo into at least two distinct components, an inner and outer halo. This result has been criticized by Schoenrich al., who claim that retrograde signature associated with is due to adoption faulty distances. We refute this claim, demonstrate photometric distances are themselves flawed because they adopted incorrect main-sequence absolute magnitude relationship from work Ivezi\'c When compared recommended relation...
Spectroscopic and photometric data for likely member stars of five Galactic globular clusters (M3, M53, M71, M92, NGC 5053) three open (M35, 2158, 6791) are processed by the current version SEGUE Stellar Parameter Pipeline (SSPP), in order to determine estimates metallicities radial velocities clusters. These results then compared values from literature. We find that mean metallicity (<[Fe/H]>) velocity (<RV>) each cluster almost all within 2{\sigma} adopted literature values; most...
Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, Extension Galactic Understanding Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained High Dispersion Spectrograph of Subaru Telescope. Most sample (approximately 80%) main-sequence turn-off stars, including dwarfs subgiants. Four cool...
We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) spectra from SDSS and SEGUE. By means star-by-star comparison with set SDSS/SEGUE available estimates based on published high-resolution analyses, we demonstrate that can measure S/N > 15 to precision better than 0.35 dex. Using measured carbon-to-iron obtained by this technique, derive frequency carbon-enhanced stars ([C/Fe] +0.7) as function [Fe/H], both other samples literature....
The chemical compositions of seven Carbon-Enhanced Metal-Poor (CEMP) turn-off stars are determined from high-resolution spectroscopy. Five them selected the SDSS/SEGUE sample metal-poor stars. effective temperatures these objects all higher than 6000 K, while their metallicities, parametrized by [Fe/H], below -2. Six our program exhibit high abundance ratios barium ([Ba/H]> +1), suggesting large contributions products former AGB companions via mass transfer across binary systems....
(Abridged) Carbon-enhanced metal-poor (CEMP) stars in the halo components of Milky Way are explored, based on accurate determinations carbon-to-iron ([C/Fe]) abundance ratios and kinematic quantities for over 30000 calibration from Sloan Digital Sky Survey (SDSS). Using our present criterion that low-metallicity exhibiting [C/Fe] ("carbonicity") excess [C/Fe]$ = +0.7$ considered CEMP stars, global frequency system \feh\ $< -1.5$ is 8%; -2.0$ it 12%; $<-2.5$ 20%. We also confirm a significant...
We present the results of a low-resolution spectral abundance study 25 stars in Boötes I dwarf spheroidal (dSph) galaxy. The data were obtained with low resolution imaging spectrometer instrument at Keck Observatory and allow us to measure [Fe/H], [C/Fe], [α/Fe] for each star. find both large spread metallicity (2.1 dex [Fe/H]) as well average this system, 〈[Fe/H]〉 = −2.59, matching previous estimates. This sample includes newly discovered extremely metal-poor star, [Fe/H] −3.8, that is one...
Due to the ever-expanding volume of observed spectroscopic data from surveys such as SDSS and LAMOST, it has become important apply artificial intelligence (AI) techniques for analysing stellar spectra solve spectral classification regression problems like determination atmospheric parameters Teff, log g, [Fe/H]. We propose an automated approach in optical region using Convolutional Neural Networks. Traditional machine learning (ML) methods with "shallow" architecture (usually up 2 hidden...
We present techniques for the estimation of stellar atmospheric parameters (Teff, , [Fe/H]) stars from SDSS/SEGUE survey. The are derived observed medium-resolution () spectra using non-linear regression models trained either on (1) pre-classified data or (2) synthetic spectra. In first case we use our to automate and generalize parametrization produced by a preliminary version Spectroscopic Parameter Pipeline (SSPP). second directly model mapping between (derived Kurucz atmospheres)...
Context.On the order of 20% very metal-poor stars in Galaxy exhibit large carbon enhancements. It is important to establish which astrophysical sites and processes are responsible for elemental abundance patterns this early Galactic population.
We have measured the amount of kinematic substructure in Galactic halo using final data set from Spaghetti project, a pencil-beam high latitude sky survey. Our sample contains 101 photometrically selected and spectroscopically confirmed giants with accurate distance, radial velocity metallicity information. developed new clustering estimator: "4distance" measure, which when applied to our leads identification 1 group 7 pairs clumped stars. The group, 6 members, can confidently be matched...